The health and vitality of the tooth is often tested by tooth sensitivity to either thermal or electrical stimulus. Electric pulp testing, which requires passing an electric current through the teeth, is the more sophisticated procedure, however, there are various drawbacks. The electric pulp tester is not a full-proof instrument and there are conditions when a tooth with a necrotic pulp or partially necrotic pulp may cause a positive response to the electrical stimulus. Conversely, a tooth with a sound vital pulp may cause no response to the electrical stimulus. Thermal pulp testing is often a much more reliable and easily performed diagnostic procedure.
A thermal test is carried out by applying either heat or cold to the tooth. Cold tests are easily performed with ice or ethyl chloride spray. A hot test is performed by either applying a heated instrument or heated gutta-percha material at a temperature of over 150 degrees F. to the tooth. In the case of a tooth with a cast crown, which is too thick to allow the heated gutta-percha to raise the temperature of the underlying tooth's structure sufficiently to react, an alternative method of producing heat is utilized. A rubber wheel mounted on a mandrel, revolving at a polishing speed, is applied against the precious metal. The friction of the rubber wheel against the tooth produces a great amount of heat quickly.
Although the thermal tests are often considered the most accurate indicator of pulp health and vitality, and especially valuable in detecting pulpitis and in helping to differentiate reversible and irreversible pulp inflammation, there is heretofore no known testing procedure or related equipment which permits the controlled, repeatable and safe application of heat to a tooth at a known temperature level. The presently known methods of heating dental materials, instruments, or creating heat by friction with a rubber wheel are all highly uncontrolled and, hence, less reliable means of accurate diagnosis.